1. Field of the Invention
The present invention relates to an electrical discharge machine for processing a work immersed in a process liquid that is water or oil and that has been stored in a process tank.
2. Description of the Related Art
In a wire electrical discharge machine, a work is processed using the portion of a wire electrode that runs between the upper and lower wire guide units. The wire electrode is guided by a roller that is fixed to the main body of the wire electrical discharge machine so as to be supplied to the wire guide units having a wire guide.
Meanwhile, the worktable on which a work is mounted moves in the X direction and in the Y direction by the instructions from the control unit and in accordance with the state of the work that is being processed. The movements in the X direction and in the Y direction are synthesized while processing progresses vis-à-vis the wire electrode supplied between the wire guide units. The wire electrode repeats the movement according to the servomechanism during the process so that a workpiece is processed to a predetermined form through electrical discharge resulting from the movements of the wire electrode and the workpiece relative to each other.
Japanese Unexamined Patent Publication 2014-180734 discloses a wire electrical discharge machine having a function of determining the state within the process tank. In this wire electrical discharge machine, it is prohibited to turn on the power supply for processing in the case where the process liquid level is lower than a predetermined height. In other words, it is prohibited to turn on the power supply for processing in such a state that a sufficient amount of process liquid has not been stored in the process tank so that an electric shock that is caused by the operator when making contact on the parts of the wire electrode and the work that are being processed or the scattering of the process liquid into the air can be prevented, and thus, the level of safety is increased.
Japanese Unexamined Patent Publication 2001-105242 discloses a process tank unit in an electrical discharge machine. The door lock is released in the case where it has been detected that the process liquid is at a predetermined level or lower by a level detection sensor for detecting the level of the process liquid within the process tank.
FIGS. 1A and 1B show the configuration of an electrical discharge machine. FIG. 1A is a diagram showing the state where there is no process liquid 22 within a process tank 6, and FIG. 1B is a diagram showing the state where a process liquid 22 is stored within the process tank 6.
During the preparation work in the electrical discharge machine, an axis feeding operation is carried out while an indicator is made to make contact with a work 4 after the work 4 has been mounted on a worktable 5 so that the inclination of the work 4 is adjusted (correction of parallelism) and the position of the work 4 is detected (positioning). In the case of a wire electrical discharge machine, a wire electrode 1 is vertically adjusted. These works are, in many cases, carried out in a state where no process liquid 22 is stored in the process tank 6 as shown in FIG. 1A. Sometimes, however, these works are carried out in a state where the process liquid 22 is stored as shown in FIG. 1B.
It is required to complete the preparation work in as short of time as possible so as to make the actual working hours of the operator as short as possible. In order to do so, it is desirable for the axis feeding of the X axis, the Y axis and the Z axis to be as fast and agile as possible. In particular, this is highly required for large-scale machines having large strokes. Usually, there are several steps of set values for the axis feeding speed, and the operator selects the axis feeding speed. In addition, some machines allow the operator to be able to preset a desired axis feeding speed. However, the set value for the axis feeding speed is fixed.
Such a problem arises that the process liquid 22 undulates and spills from the process tank 6 in the case where an axis feeding operation is carried out when the level of the process liquid 22 stored in the process tank 6 is high. It is possible for the operator to slip on the process liquid 22 when it has been spilt onto the floor. Here, electrical discharge machines include a type where the process tank 6 is movable and a type where the process tank 6 is still but the head unit or the guide unit is movable instead (in some cases they both are movable along different axes). The above-described problem appears mainly with the former type, but not in a small number of cases, the same phenomenon could happen in the latter type due to the occurrence of the flow of the process liquid.
Japanese Unexamined Patent Publication 2014-180734 and Japanese Unexamined Patent Publication 2001-105242 are both examples of the prior art where a certain operation is carried out on the basis of the level of the process liquid. However, neither relates to the axis feeding speed.